Global map of the sickle cell gene supports 'malaria hypothesis'

Nov 02, 2010

These are maps showing the distribution of the HbS "sickle cell gene" and the endemicity of malaria. Credit: Malaria Atlas Project

At a global scale, the sickle cell gene is most commonly found in areas with historically high levels of malaria, adding geographical support to the hypothesis that the gene, whilst potentially deadly, avoids disappearing through natural selection by providing protection against malaria.

In a study funded by the Wellcome Trust, geographers, biologists and statisticians at the University of Oxford, together with colleagues from the KEMRI-Wellcome Trust Programme in Kenya, have produced the first detailed global map showing the distribution of the sickle cell gene. The results are published today in open access in the journal Nature Communications.

Haemoglobin S (HbS) is known to cause sickle cell disease, which is usually fatal if untreated. Natural selection suggests that such a disadvantageous gene should not survive, yet it is common in people of African, Mediterranean and Indian origin.

More than sixty years ago, researchers observed that the sickle cell gene tended to be more common in populations living in, or originating from, areas of high malaria prevalence. This led to the 'malaria hypothesis', which suggested that, although deadly when inherited from both parents, the gene provided a degree of protection from malaria in children inheriting it from just one parent. This protective advantage was strong enough in areas of intense malaria transmission for the gene to survive.

The malaria hypothesis has since been supported by both population and laboratory studies, but the original observations of a geographical overlap between frequency of the gene and malaria prevalence have never been tested beyond simple visual comparisons at the global scale.

To address this, Dr Fred Piel and colleagues collated all the information currently accessible on the occurrence of the sickle cell gene in native populations worldwide and, using modern mapping techniques, created a map of the global frequency of this gene. The map was then compared with the distribution and intensity of malaria before widespread malaria control.

The study showed that the sickle cell gene is most common in sub-Saharan Africa, the Middle East and India, and that the areas of high frequency of this gene are coincident with historically high levels of malaria, thus confirming that the malaria hypothesis is correct at the global scale.

"This study highlights the first steps in our efforts to create an open-access, online database of the frequency of various inherited blood disorders," says lead author Dr Piel, from the University of Oxford. "Such databases will help improving estimates of their public health burden and guide where resources would be best applied."

More information: The sickle frequency map was created as part of the activities of the Malaria Atlas Project, a multinational research collaboration funded primarily by the Wellcome Trust. Further information about the Malaria Atlas Project can be found at www.map.ox.ac.uk

A new evidence-based global distribution map of Plasmodium vivax malaria, published August 3 in the open-access journal PLoS Neglected Tropical Diseases, is used to estimate that 2.85 billion people lived at risk of infec ...

About 35 percent of the world’s population is at risk of contracting deadly malaria, but many people are at a lower risk than previously thought, raising hope that the disease could be seriously reduced ...

A new study by the Malaria in Pregnancy Consortium has estimated that more than 125 million pregnancies around the world are at risk from malaria every year. Until now, estimates have only been available for endemic areas ...

Recommended for you

(HealthDay)—For patients with facet joint arthropathy, platelet-rich plasma (PRP) has a short-term positive impact, according to a study presented at the annual meeting of the American Academy of Pain Medicine, ...

Both traditional and HIV-related risk factors can predict the likelihood of developing chronic kidney disease (CKD), according to a study published this week in PLOS Medicine. In the study, Amanda Mocroft, of University Colleg ...

New research at the University of Michigan offers evidence that a drug being developed to treat osteoporosis may also be useful for treating osteogenesis imperfecta or brittle bone disease, a rare but potentially debilitating ...